The invention relates to a system for automatically controlling the gauge of rod being rolled in the finishing block of a rod rolling mill.
Rolling mills produce rod by rolling heated billets through a series of roll stands. As described for example in U.S. Pat. No. 3,336,781, the final or "finishing" stands are conventionally grouped into a finishing block. The roll axes of successive roll stands in the finishing block are orientated 90 degrees in relation to each other in order to avoid having to twist the product. As the rod passes through each pair of rolls, its cross-sectional area is progressively reduced. The roll partings of each pair of rolls are adjustable to control the reductions being taken.
The rod dimensions are determined either by an on line gauge measurement or by cropping rod samples which are measured off line. When an off-gauge situation is encountered in the rolling of steel rod, depending on the severity of the problem, the remaining billet length will either continue to be rolled through the finishing block, or it will be diverted to crop shears for subdivision into scrap lengths. Thereafter, roll parting adjustments will be performed under "no load" conditions before rolling is resumed. Thus, in conventional mills, the inherent time lag between detection of an off-gauge situation and the performance of required corrections results either in the rolling of substantial amounts of off-gauge product, or in aggravated circumstances, the scrapping of valuable product. Moreover, the manual performance of roll parting adjustments requires highly skilled and attentive operating personnel. Where such personnel are unavailable, the operating efficiency of the mill is reduced even further. There is, therefore, a need for a system which will automatically determine when a rod is out of tolerance and promptly effect the necessary roll parting adjustments while the mill continues to roll product and without operator intervention.
The present invention is directed to a system for monitoring the dimensions of a product passing through the finishing block or a rod rolling mill and for automatically controlling the roll partings of at least one pair of rolls in the finishing block based on the aforesaid monitored dimensions. The roll partings are adjusted under load, thereby eliminating the substantial time lag currently experienced in conventional installations.
Broadly, the invention embodies a control system which monitors the dimensions of the product entering and leaving the finishing block. The system includes a CPU and peripheral devices which communicate via compatible interfaces. A first data station reads the dimensions of the product prior to its entering the first finishing stand. If these read dimensions exceed pre-established tolerance limits, an alarm condition is created. Based on the extent that the product is out of tolerance, a decision is made as to whether to continue to roll the rod through the finishing stands, or alternatively have the rod bypass the finishing stands for cropping into scrap lengths.
From each of the finishing stands, information is provided to the CPU corresponding to: drive shaft torque; separating force; roll shaft bearing temperature; and, the parting dimension between rolls. From the CPU, commands are sent to a position sensor to control roll parting. Drive shaft torque and roll separating force jointly correspond to the work load of the rolls. If this load exceeds a pre-established limit, an alarm condition is created. If the bearing temperature exceeds a pre-established limit, then an alarm condition is created.
A second data station reads the dimensions of the product after it leaves the last finishing stand. If these dimensions exceed pre-established limits, then an analysis is made to determine if the roll partings of the finishing stand can be adjusted to bring the product rod within tolerance. Depending upon the amount the product is out of tolerance the parting dimension(s) of the rolls of only one finishing stand, some of the finishing stands or all of the finishing stands may be adjusted. The difference between the in tolerance (target) dimension and the out-of-tolerance dimension is calculated and used as the dimension (calculated adjustment) the rolls of the last finishing stand must be adjusted to bring the product into tolerance. The work to be performed on the product is distributed among the finishing stands. Progressively smaller roll parting adjustments (cascade adjustments) for the finishing stands preceeding the last finishing stand are calculated based on the calculated adjustment to the rolls of the last finishing stand. Preferably, these cascaded adjustments are in reciprocal geometric progression.
After the cascade adjustments are calculated, a determination is made to ascertain if the rolls can actually be adjusted the calculated amount. This determination is a two step procedure. The first step analyses whether or not the proposed adjustments are within reasonable limits. If they are, then second step analyses whether the new roll partings are achievable.
The first step compares the calculated adjustments to be made to the roll partings of each finishing stand to pre-established limits. The limits function as a window to exclude unacceptable data. If the limits are exceeded an alarm condition is created. If these limits are not exceeded then the second step compares the calculated adjustments for each of the roll partings to the actual position of the rolls to determine if the rolls of each finishing stand are capable of opening or closing the actual distance required. If they are, then the roll parting adjustments are made.
This sequence of steps calculates what adjustments to the rolls are necessary to bring the product into tolerance and whether or not the roll parting adjustments are possible. The roll parting adjustments of all finishing stands are based on a reciprocal geometric progression from the last finishing stand to the first, thereby distributing among the finishing stands the work which must be performed upon the product to bring the product into tolerance. If the adjustments are possible, then the roll parting between the rolls of at least one finishing stand is adjusted. If the adjustments are not possible, then an alarm condition is created.
The invention provides for on line roll parting adjustments in a twist-free finishing mill. The response time between detection of out of tolerance product and roll parting adjustments is within seconds, and the roll parting adjustments are made under load.